Within a system to mount parts to a substrate, a substrate loading machine, a printing machine, a surface mount machine, an inspection machine, a substrate unloading machine and the like are arranged next to each other from the upstream side toward the downstream side of a substrate transportation direction along a transportation line for transporting substrates. Among these line machines, the printing machine, the surface mount machine and the inspection machine execute predetermined processing while ejecting air of a positive pressure from nozzles. The surface mount machine according to Japanese Patent Application No. 2008-27986 (FIG. 1) for instance is equipped with two types of air circuits which supply air of a positive pressure to a suction nozzle. One of them is to generate air of a suction nozzle releasing positive pressure, while the other one is to generate air of a weaker positive pressure (hereinafter “weak positive pressure”) than the suction nozzle releasing positive pressure. Air of the weak positive pressure is applied to the suction nozzle to prevent fine dust and the like from adhering to a nozzle tip before the suction nozzles sucks a part. Even after suction of a part by the suction nozzle, air of the weak positive pressure is applied to the suction nozzle, thereby realizing a function of smoothly releasing the part from the suction nozzle. Meanwhile, at the time of exchanging the suction nozzle, air of a suction nozzle releasing positive pressure is applied to the suction nozzle and the suction nozzle is smoothly released.